Roof Pitch Calculator to convert roof rise and run into an x-in-12 pitch, roof angle in degrees, percentage slope, slope multiplier, and rafter length factor for roofing and construction planning.
Home & Construction Calculators
Calculate roof pitch, angle, percentage slope, and slope multiplier from rise and run.
Use the same unit for rise and run. A standard 6:12 roof rises 6 units for every 12 units of horizontal run.
About the Roof Pitch Calculator
Roof pitch describes how much a roof rises over a horizontal run. This calculator accepts any consistent rise and run measurements, reduces them to a slope ratio, converts the slope to the common x-in-12 roofing format, and reports the roof angle, percentage grade, slope multiplier, and diagonal length for 12 units of run.
Formula and assumptions
Slope ratio = rise ÷ run. Pitch per 12 = (rise ÷ run) × 12. Roof angle = arctan(rise ÷ run). Percentage slope = (rise ÷ run) × 100. Slope multiplier = √(rise² + run²) ÷ run. Diagonal length per 12 units of run = √(12² + pitch-per-12²).
Worked example
With a rise of 6 and run of 12, the roof is a 6:12 pitch. The angle is approximately 26.57°, the percentage slope is 50%, and the slope multiplier is about 1.118. For every 12 units of horizontal run, the sloped rafter length is approximately 13.42 units.
Measurement checklist
- Measure rise vertically and run horizontally.
- Use the same unit for both measurements.
- Use half the building span for the run of a symmetrical gable roof.
- Do not include decorative overhangs unless they are part of the measured run.
Manual calculation steps
- Divide the vertical rise by the horizontal run.
- Multiply the ratio by 12 for the x-in-12 pitch.
- Use arctangent to calculate the angle.
- Multiply the ratio by 100 for percentage slope.
- Calculate the hypotenuse-to-run slope multiplier.
- Use the multiplier when converting footprint area to sloped area.
Frequently asked questions
What does a 6:12 roof pitch mean?
It means the roof rises 6 units vertically for every 12 units of horizontal run. The measurement unit can be inches, centimeters, or another consistent unit.
How is roof pitch different from roof angle?
Pitch is normally expressed as rise over run, while roof angle expresses the same slope in degrees from horizontal.
What is the slope multiplier used for?
Multiply the horizontal projected area or run by the slope multiplier to estimate the corresponding sloped surface measurement.
Common mistakes
- Measuring the run along the roof instead of horizontally.
- Using the full building span instead of half-span for one roof side.
- Mixing inches, feet, centimeters, or meters.
- Confusing percentage slope with degrees.